Leak protected heat exchanger

ABSTRACT

A plate and fin type heat exchanger in which different flowing fluids are placed in a segregated heat transfer relation and in which provision is made to deny opportunity for a leaked fluid from one flow or circuit to join or mix with fluid of another flow or circuit. A concept of vented buffer zones is used to protect against leakage through plate elements and through defined joints between plate and spacer elements. The concept allows and provides for relatively simple manifolding and for fabrication to conventional configurations using for the most part standard easily manufactured parts.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to fluid to fluid heat exchangers andparticularly to structural features thereof reducing the likelihood offluid mixing as may result from leakage caused by wear, corrosion,imperfect braze joints or the like.

2. Description of the Prior Art

In a common form of fluid to fluid heat exchanger, plate elements andspacer elements are effectively stacked or assembled so that they definemultiple superimposing or side by side fluid flow passages. Through useof applied manifolds, or other means, first and second fluids aredirected through alternating passages, with a transfer of heat takingplace from the fluid of higher temperature to the fluid of lowertemperature through the plate separating adjacent passages. Usually astrip of corrugated fin material is placed in each flow passage to makethe heat transfer process more efficient and to promote structuralstrength and rigidity. After assembly, and in a preferred joiningprocess, parts are united into a one-piece structure by a brazingprocess in which plate elements are made fast to spacer elements uponwhich they superimpose and the peaks and valleys of the corrugated finmaterial attach to overlying and underlying plate elements. In variousways, braze material is introduced at joints where parts contact oneanother, and, in the presence of heat and pressure, the material flowsto fill the defined joints. The braze connection is multi-functional. Itconnects the parts in a uniform assembly. It provides for heat flow withminimal thermal resistance, and, it seals the defined joints againstfluid leaks. Since at least one of the flowing fluids is often underrelatively high pressure, great care is usually taken to insure that thebraze joints are sound and well sealed.

Heat exchangers as described have enjoyed a long commercial success.They lend themselves particularly well to fabrication using light weightmetals. They are easy to manufacture, all of the braze joints beingeffected in a single operation, and they are highly efficient.

However, use requirements are sometimes quite severe. In someapplications, for example, even minor amounts of leakage from one flowcircuit to another cannot be tolerated. When made under carefullycontrolled conditions and subjected to repeated inspections, a leakproof heat exchanger can be produced. Such manufacture may not always beeconomically feasible, however, and is in any event no guarantee thatleaks will not develop in service. Common causes of leaks are weaklybrazed joints not adequately resistant to vibration and pressurestresses, and imperfections in a plate element developing pin hole leaksin the manufacturing process or as a result of corrosion. One or both ofthe fluids put through the heat exchanger may be corrosive or entraincorrosive materials. One practiced brazing process is carried out in asalt bath and, with occasionally imperfect results, subsequent flushingprocedures are used to wash salt residue from interior passages.

In addition to efforts made to make the heat exchanger leak proof,concurrent efforts have been made to render leaks harmless, that is, toprevent fluid interchange from one flow circuit to another. In one priorart example, shown in P. Bathla U.S. Pat. No. 3,825,061, issued July 23,1974, plate elements are configured as unitary tubes leaving the fluidconducted therethrough no opportunity to leak through brazed joints.Also, through a use of superstructure built up at either end of the heatexchanger, drained collection chambers are provided for fluid which mayleak past those braze joints which at other locations separate the fluidcircuits. The prior art construction adequately serves its intendedpurpose. Certain disadvantages and limitations attend its use, however.Thus, the integrally formed tubes and components comprising the endsuperstructure are not usual or conventional in plate and finconstructions. Their use adds substantially to the difficulties and costof manufacture. Further, the prior art device does not take into accountor provide for leakage through plate elements defining the flowpassages. As seen above, these can be the source of leaks as well as canthe braze joints.

SUMMARY OF THE INVENTION

This invention presents a leak protected heat exhanger overcomingdisadvantages and limitations of the known prior art. The coreconstruction is made up of standard, readily available parts. The partsare, moreover, assembled in a conventional manner requiring no specialskills and the resulting structure is free of unconventionalsuperstructure or the like. The core construction features a use ofbuffer zones or collection chambers totally integrated into basicoutlines of the core unit. They include buffer zones between flowpassages for the different flowing fluids and buffer zones surroundingthe flow passage of a high temperature, high pressure fluid. Bufferzones are communicated to the core exterior through a face thereof. Arelatively simple manifold is fixed to the core at that face andincludes means to conduct the high pressure, high temperature fluid tothe face as well as a vent chamber to receive leaked fluids.

An object of the invention is to provide a leak protected heat exchangersubstantially as above set forth.

Other objects and structural details of the invention will appear fromthe following description when read in connection with the accompanyingdrawing, wherein:

FIG. 1 is a top plan view of a leak protected heat exchanger inaccordance with the invention embodiment;

FIG. 2 is a view in longitudinal section taken substantially along theline 2--2 of FIG. 1;

FIG. 3 is a view in longitudinal section taken substantially along theline 3--3 of FIG. 1;

FIG. 4 is a fragmentary view in longitudinal section taken substantiallyalong the line 4--4 of FIG. 1;

FIG. 5 is a view in cross section taken substantially along the line5--5 of FIG. 2;

FIG. 6 is a view in perspective, and partly fragmentary, of the heatexchanger; and

FIG. 7 is a detail view in cross section taken substantially along theline 7--7 of FIG. 4.

Referring to the drawings, a heat exchanger assembly according to theinvention embodiment illustrated is adapted to be submerged in a body ofliquid, as in a fuel tank in a fuel burning engine system. The liquidhas access to through open passages or passes in the heat exchanger andin those passages is in a heat transfer relation to another fluid whichin a separate, segregated circuit is caused to flow through other heatexchanger passages or passes. In the present instance the liquid servesas a coolant for the relatively hot fluid of the segregated circuit.Temperature differentials provide for an induced convection flow of theliquid in through, open passages of the heat exchanger. The relativelyhot fluid flows under externally generated system pressure. Forconvenience of description, the liquid will hereinafter be referred toas fuel and the relatively hot fluid as air, for example high pressure,high temperature bleed air as drawn from a gas turbine engine to performvarious functions in an aircraft or like environment.

The heat exchanger comprises a core 10 and a manifold 11. The core 10has a rectangular configuration. The manifold 11 is fixed, as bywelding, to one end face of the core. Top and bottom core surfaces, asviewed in FIG. 1, are defined by respective flat plates or core sheets12 and 13. Between the core sheets 12 and 13 are multiple spacerelements and other flat plates or tube sheets, to be more particularlyidentified hereinafter, cooperating to define the several describedpassages. That face of the heat exchanger to which manifold 11 attachesmay be designated as a face 14 in part formed by corresponding ends ofthe plates 12 and 13.

Immediately adjacent to the plate 12 are longitudinally spaced apartspacer elements 15 and 16, parallel to one another. The former positionsat and in part defines the face 14 and in length is substantiallycoextensive with the width of plate 12. The latter in part defines anopposite end face 17 of the heat exhanger core. The elements 15 and 16space plate 12 from a tube plate or sheet 18 configured like plate 12but made of relatively thinner sheet material. Together, the plates 12and 18 and spacer elements 15 and 16 form a passage 19 open from top tobottom of the core, or from side to side as seen in FIG. 1. In thepassage 19 is a corrugated strip of fin material 21.

The tube sheet 18 overlies (as seen in FIG. 1) a like sheet 22 and isspaced therefrom by a pair of spacer elements 23 and 24 (FIG. 3). Theformer has a U-shape, its closed end positioning at and in part definingthe face 17 and its open end positioning at and in part defining theface 14. Element 24 is in the same plane as element 23 and disposestransversely across the open end thereof. Its length, however, issomewhat less than the width of element 23 and, when positionedcentrally of the open arms of element 23, leaves spaced apart apertures25 and 26 opening through face 14. Together, the tube sheets 18 and 22and spacer elements 23 and 24 define a space 27 which for reasons whichwill later more clearly appear, is designated a collection chamber. Thechamber 27 is open to the exterior of the heat exchanger core throughthe apertures 25-26 in core face 14. The spacer elements 23 and 24 areshort in height, as compared to spacer elements 15 and 16, so that tubesheets 18 and 22 are much more closely adjacent than are side wall 12and tube sheet 18. The chamber 27 is, therefore, shallow or narrow ascompared to passage 19.

The tube sheet 22 overlies another sheet 18 and is spaced therefrom bymultiple spacer elements 28, 29 and 31 (FIG. 2). Element 28 isstructured and orients like spacer element 23. It has a U-shape, itsclosed end positioning at and in part defining the face 17 and its openend positioning at and in part defining the face 14. Element 29 is inthe same plane as element 28 and is similarly structured but madesmaller so as to nest within and in a spaced relation to element 28. Thearrangement leaves a space 32, which may also be regarded as acollection chamber, between elements 28 and 29. The open ends of thespacer elements 28 and 29, along with overlying and underlying sheets 22and 18, define apertures 33 and 34 by which chamber 32 opens throughface 14. The spacer element 31 is positioned centrally of and isembraced by the arms of element 29. Its one end terminates at face 14.Its opposite end terminates short of the closed end of element 29. Theelement 31 has the character of a divider and in conjunction withelement 29 and overlying and underlying sheets 22 and 18 forms a fluidflow passage 35 having entrance and exit ends 36 and 37 at the face 14.Thus, fluid, in the present instance air, directed to entrance 36, flowslongitudinally of passage 35 to one side of divider 31 and thentransversely of the passage across the opposite or inner end of thedivider to the other side thereof where it returns longitudinally of thepassages to exit 37. The height of spacer elements 28, 29 and 31corresponds approximately to that of spacer elements 15 and 16. Withinthe passage 35 are mating strips 38, 39 and 41 of corrugated finmaterial.

Below flow passageway 35 and collection chamber 32, as seen in FIG. 1,are means defining another collection chamber 27 and below that meansdefining another fuel passage 19, the pattern as described beingrepeated any desired number of times to complete a core assembly. In theillustrated instance, four fuel passages 19 are produced and three airpassages 35, the air passages being in an alternating relation to thefuel passages and being separated therefrom by intervening collectionchambers 27. A fuel passage 19 occurs adjacent each plate 12 and 13 sothat no air passage lies adjacent to a side wall of the core. Theseveral air and fuel passages and intervening collection chambers 29 areidentical to one another.

To assemble the heat exchanger core, individual component elements arestacked one upon another, this being expeditiously done in a jig orfixture.

In the process, spacer elements 15-16, 23-24 and 28, 29 and 31 areeffectively interposed between a core sheet and a tube sheet or betweena pair of tube sheets. Also in the assembly process, or separately,braze material is introduced into joints as represented by areas ofcontact of sheet elements with spacer elements. In the presence of thebraze material, parts are pressured into close intimate contact and thetemperature of the assembled core raised to the melting point of thebraze material. The braze material flows to fill the described joints,and, upon the core assembly being allowed to cool, component parts willbe found to be joined together into a unitary whole by meansconstituting a seal and a bond. According to one brazing technique,plate and sheet elements 12-13 and 18 and 22 are clad with a brazematerial, this technique being particularly useful when it is desiredthat peaks and valleys of the fin material be brazed to overlying andunderlying sheet elements.

The manifold 11 is made in any appropriate manner to provide an interiorvent chamber 42 (FIG. 2) and flow tubes 43 and 44 extending through thechamber 42. In the illustrated instance the manifold is made of acombination of machined and cast parts welded into unit form. An angularbody 45 provides the larger portion of chamber 42 and at its one end hasperimeter contact with face 14 of the core 10. Chamber 42 opens throughsuch one end and so opens upon face 14 in communicating relation withapertures 25-26 and 33-34. The opposite end of body 45 has fixed theretoan extension portion 46, comprising an interior chamber 42a, which is apart of vent chamber 42, and openings 47, 48 and 49 to outside of themanifold. Opening 49 communicates directly with chamber 42a andtherefore with chamber 42. The openings 47 and 48 accommodate thepresence of open ends of respective tubes 43 and 44. The latter extendthrough chamber 42a and into chamber 42 where they are commonly joinedto a generally rectangular wall 51 (FIG. 5) in concentric inwardlyspaced relation to that perimeter portion of body 45 contacting face 14.The wall 51 has a perimeter portion substantially bridging the spacebetween spacer elements 29 and has a recessed frontal surface 52 openingupon face 14. The recessed surface 52 is split by a centrallypositioning rib 53 of the wall 51 to form therein separated chambers 54and 55. Tube 43 opens through the wall into chamber 54. Tube 44 opensthrough the wall into chamber 55. The divider rib 53 registers with theseveral divider elements 31, with chambers 54 and 55 aligning with andhaving common communication with the several air flow entrances 36 andexits 37 respectively.

The manifold 11 is secured as by welding to the face 14 of the heatexchanger cone. Side walls 12 and 13, spacer elements which terminate atthe face 14, and spacer elements (elements 15) which position at andtransversely of the face 14, provide abutment surfaces to whichperimeter wall portions of the manifold may be welded. Referring to thespacer elements 15, as shown in FIGS. 6 and 7, each has over a portionof its length intermediate its ends upper and lower longitudinal groovesor recesses 56 and 57. Where these grooves terminate adjacent to ends ofthe element, the element further is cut by slots 58 and 59 which are incommon communication with grooves 56 and 57 and open, moreover, throughface 14. The spacing of slots 58 and 59 is such as to locate themoutside the bounds of manifold wall 51 whereby they communicate, alongwith apertures 25-26 and 33-34, with manifold vent chamber 42.

In the manifold, opening 49 connects vent chamber 42-42a to ambientsurroundings or to a suitable low pressure drain. Openings 47 and 48, ormore particularly tubes 43 and 44 installed therein, are connected in asystem flowing high pressure, high temperature air. Tube 43 serves asthe air inlet and conducts air to chamber 54 where it has simultaneousaccess to the inlets 36 of all air flow passages 35 in the core 10.Flowing through the several passages 35, in the route compelled bydividers 31, the air reaches exits 37 and discharges into chamber 55 tobe conducted through and out of the manifold by the way of air outlettube 44. Flow of the heated air in passage 35 takes place in thepresence of relatively cool fuel in passages 19. A conducted transfer ofheat takes place across the sheets 18 and 22 which separate the fuel andair passages with a consequent cooling of the flowing air. If desired, afin material or the like may be placed in chambers 27, in contact withoverlying and underlying tube sheets, for better heat conductance.

In the event of developed pin hole leaks or the like in tube sheets 18or 22, leaked fluid, whether from the air or fuel circuit, has accessonly to a collection chamber 27 and not to fluid of the other circuit.In the event of leakage at joints where the tube sheets contact spacerelements 28 and 29, leaking air has access only to an intermediatechamber 32 and not to the fuel circuit. In the event of leakage atjoints where side walls or tube sheets contact spacer elements 15,leaking fuel reaches the groove 56 or 57 and then slot 58 or 59 outsidethe air flow circuit. All leaked fluid, whether in collection chambers27, intermediate chambers 32 or grooves 56-57 are communicated throughcore face 14 to vent chamber 42 of the manifold.

A particular invention embodiment has been disclosed for illustrationpurposes. It will be evident that modifications within the skill ofthose versed in the art may be made without departing from inventionconcepts. The use of integrated buffer zones within a heat exchangercore as here taught is believed to be broadly applicable in plate andfin type heat exchangers. Other manifolding arrangements are possible,and, of course, the fuel could be manifolded into and out of the core ifthe fuel circuit were intended to be a closed system.

In the claims, the fluid flowing passages 19 and 35 are termed "passes"in order better to distinguish from the marginal vent passage 32.

Spacer elements other than elements 31, since they occur at or adjacentto marginal edges of the heat exchanger core, may be termed marginalspacer elements.

What is claimed is:
 1. A leak protected heat exchanger, including anassembly of stacked plate and fin and spacer elements defining layeredflow passes for first and second fluids and between adjacent flow passesor different fluid flow collection chambers for receiving leaked fluidfrom said flow passes, means for separately communicating adjacent flowpasses of different fluid flow with said first and second fluids, andmeans for venting said collection chambers, said stacked elementsproducing an assembly of generally angular configuration including anexternal face through which flow passes associated with a first fluidopen and through which said collection chambers open, and including amanifold applied to said face structured to include passage meanscommunicating with said first fluid passes and to include a vent chamberinto which said collection chambers open.
 2. A leak protected heatexchanger according to claim 1, wherein said flow passes and saidcollection chambers are defined by plate elements spaced apart by saidspacer elements, the layered passes flowing said first fluid includingmarginal spacer elements forming with adjacent plate elements a ventpassage opening through said assembly face into said vent chamber ofsaid manifold.
 3. A leak protected heat exchanger according to claim 2,said vent passage being formed by a pair of marginal spacer elements ina parallel spaced apart relation, said plate elements superposing onsaid spacer elements.
 4. A leak protected heat exchanger according toclaim 2, the layered flow passes defining second fluid passes beingdefined by plate elements spaced apart by longitudinally spaced apartspacer elements including a spacer element located at and forming a partof said assembly external face, the said spacer element of said facebeing configured to provide a passage at surfaces thereof contacted bysaid plate elements communicating through said external face with thesaid vent chamber in said manifold.
 5. A leak protected heat exchanger,including an assembly of stacked plate and fin and spacer elementsdefining layered flow passes for first and second fluid to pass in heattransfer relation to one another, means defining a vented buffer zonebetween first and second fluid flow passes receiving fluid leakedthrough said plate elements, means defining a vented buffer zone forfluids leaked through spacer element-plate element joints in first fluidflow passes, means defining a vented buffer zone for fluids leakedthrough spacer element-plate element joints in second fluid flow passes,said assembly being configured to provide an external face through whichsaid buffer zones open, and including a manifold applied to said faceincorporating a vent chamber in common communication with said bufferzones, said first fluid flow passes opening through said external face,and said manifold having first fluid flow passage means communicatingwith said first fluid flow passes to the exclusion of said buffer zones.6. A leak protected heat exchanger according to claim 5, said meansdefining a vented buffer zone between first and second fluid flow passesproviding a collection chamber between and substantially coextensivewith said fluid flow passes.
 7. A leak protected heat exchangeraccording to claim 5, said means defining a vented buffer zone forfluids leaked through joints of said first fluid flow passes providing amarginal vent passage in substantially surrounding relation to a firstfluid flow pass in the plane thereof.
 8. A leak protected heat exchangeraccording to claim 5, said means defining a vented buffer zone forfluids leaked through joints at said second fluid flow passes providinga vent passage within a spacer element at least at one end of a secondfluid flow pass.
 9. A leak protected heat exchanger, including anassembly of stacked plates and spacer elements defining layered flowpasses for first and second fluids to pass in heat transfer relation toone another, plate elements being separated by marginal spacer elementsand defining therewith plate element-spacer element joints, other spacerelements between adjacent first and second fluid flow passes defining acollection chamber for fluids leaked from said fluid flow passes throughplate elements separating said fluid flow passes from said collectionchamber, said other spacer elements being in a bounding enclosingrelation to said collection chamber with provision being made for aventing of said collection chamber therethrough, said spacer elementsbeing constructed and arranged to provide interior passages into whichfluids leaked through said plate element-spacer element joints haveaccess, the heat exchanger having an exterior face for manifoldattachment through which face said collection chamber and said interiorpassages separately open.
 10. A leak protected heat exchanger, includingan assembly of stacked plates and spacer elements defining layered flowpasses for first and second fluids to pass in heat transfer relation toone another, and defining between adjacent first and second fluid flowpasses collection chambers for fluids leaked from said fluid flow passesthrough plate elements separating adjacent fluid flow passes from acollection chamber, the heat exchanger having an exterior face throughwhich a first flowing fluid has access to first fluid flow passes, andmeans for venting said collection chambers through said exterior face,the access to said first fluid flow passes and said venting means beingseparated so that manifolding means applied to said face may provide forseparate communication with said first fluid flow passes and with saidventing means.
 11. A leak protected heat exchanger according to claim10, said spacer elements defining with adjacent contacting plates spacerelement-plate joints, said spacer elements being constructed andarranged to provide interior passages into which fluids leaked throughsaid joints from first and second fluid passes have access, saidinterior passages opening through said exterior face in a separatedrelation to the means venting said collection chambers.